1. Field of the Invention
The invention pertains to apparatus for generating a sequential pulse train of high frequency electromagnetic signals having a duration on the order of one nanosecond or less and specifically to generators in which the output pulse sequence and the pulse width of the individual pulses can be controlled electronically without mechanically modifying the structure of the apparatus.
2. Description of the Prior Art
U.S. Pat. No. 3,612,899 entitled "Generator For Short-Duration High Frequency Pulse Signals", issued on Oct. 12, 1971 in the names of G. F. Ross et al and assigned to the assignee of the subject application, discloses a pulse forming network which includes open and shorted stubs for furnishing a few short pulses from a longer pulse or one short pulse. The usefulness of this prior art apparatus decreases as the desired number of individual pulses increases because the amplitude of the output pulse decreases with the number of junctions so that for N junctions the output pulse is decreased by 2.sup.-.sup.N. Furthermore, since the pulse forming network is passive, the spectral density in the output pulses must always remain equal to or less than the spectral density of the input pulse. In addition, each desired sequence of pulses requires a separate pulse forming network so that a change in the desired sequence of pulses can only be produced by replacing the pulse forming network.
U.S. Pat. No. 3,484,619 entitled "Radio Frequency Generators", issued on Dec. 16, 1969 in the name of J. M. Proud, Jr. and assigned to Ikor Inc. teaches an apparatus for producing pulse sequences from a plurality of transmission line segments separated by a series of spark gaps which are operated as switches. This spark gap device is used exclusively for generating very high power levels on the order of 20 kV which is impractical for use in applications requiring lower voltage levels. In addition, the individual pulse widths may only be adjusted by the time consuming process of altering the electrode spacing or the gas pressure and the output sequence of pulses can only be altered by mechanically replacing the actual hardward comprising the transmission line segments.
U.S. Pat. No. 3,832,568, entitled "Circuit For Generating A Single High Voltage Subnanosecond Baseband Pulse", issued on Aug. 15, 1974 in the name of C. C. Wang and assigned to the same assignee as the subject application, discloses a circuit including a step recovery diode for producing a single subnano-second baseband pulse in response to a longer duration pulse input.